In recent years, a method that uses a network boot system is widespread to deploy operating systems (hereinafter referred to as an “OS”) for a large number of client terminals (hereinafter referred to as a “terminal”). (Patent Document 1) The network boot system is characterized that “OS image data”, which is stored in network boot server as a disk image including the OS for the terminals, is mounted directly to each terminal through a high speed network, such as a Local Area Network (LAN) and is shared by the terminals. Then, its largest advantage is immediate reflection of updated content of the OS image data (more precisely, updating after each terminal is rebooted next time) when the OS image data is updated on the network boot server side. Furthermore, since the network boot server is required to manage only one OS image data for the terminal, generation-management of a plurality of versions is also relatively easily achieved.
The network boot system is supposed that one network boot server is connected to a large number of terminals (“1:N connection”). It is a prerequisite that each terminal is connected to a high speed network environment from the boot time. A large scale network boot system having more than 50 terminals, for example, is not expected to provide a comfortable operation environment for practical use, if the LAN environment is not connected by a “Gigabit” high speed network. A spread of the network boot system in recent years is due in large part to that of this very high speed network.
On the other hand, there is a known technique that a common OS image data is processed as master data and its copy is distributed and each terminal is booted by using the copy (hereinafter referred to as a “disk distribution technique” in this present invention). (Patent Document 2) Although the disk distribution technique has provided disk-like recording media, such as DVD and CD (from which the name of the disk distribution technique is derived), to deliver (distribute) a boot image of OS, a method for distributing data from server to client terminal through the network, etc. is also adopted in recent years. A boot method (like the disk distribution technique) that the terminals can be sufficiently booted in a local environment even if the terminals do not connect the network is called “local boot” against “network boot” herein.